1) Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to a copier, a printer, and a facsimile using an electro-photographic process.
2) Description of the Related Art
An image forming apparatus charges a photoreceptor by a charging member, and forms a latent image using a laser light, and forms a toner image by developing the latent image using a toner that is not greater than 10 xcexcm in grain size. The image forming apparatus transfers the toner image to a transfer paper, and registers the image on the transfer paper by fusing and fixing the image using a heat roller. If the charging member is provided in contact with or adjacent to the photoreceptor, an electric resistance of the charging member changes, because foreign substances adhere to a surface of the charging member as the charging member is used for a long time. Thereby, an abnormal image occurs due to an uneven charging, an insufficient charging, and a faulty charging. The foreign substances include residual toner on the photoreceptor, or paper powder produced from the transfer paper. The photoreceptor is provided with a photoreceptor cleaning unit to remove the foreign substances. However, if grains of the foreign substances are smaller or closer to round in shape, the foreign substances pass through the photoreceptor cleaning unit, and gradually adhere to a surface of the charging member that is located downstream the cleaning unit. Further, the paper powder, the toner, and dust, floating in the image forming apparatus, also gradually adhere to the surface of the charging member, and change the electric resistance of the charging member as the charging member is used for a long time to induce the abnormal image.
To cope with the abnormal image, for example, Japanese Patent Application Laid-Open No. HEI 8-123140 discloses a charging device that removes the foreign substances from the surface of the charging member by pressing a pad-shaped material onto the member.
Further, Japanese Patent Application Laid-Open No. HEI 11-288150 discloses a charging roller cleaning unit provided with a flexible member. The charging roller cleaning unit cleans a surface of the charging roller by a surface contact of the flexible member with the charging roller.
However, according to Japanese Patent Application Laid-Open No. HEI 8-123140, the pad-shaped material is pressed onto the charging member capturing the foreign substances. If the foreign substances include the toner or other additives, the substances are rubbed against the charging member. If the charging member is used for a long time, a sheet of thin film is formed on the charging member by effects of a press and a frictional heat. Thus, the thin film can damage a charging function of the charging member. Further, it is difficult to keep an effectiveness of a cleaning effect of the pad for a long period of time, because a contact area of the pad with the charging member that actually contributes to the cleaning of the charging member is small. One idea is to increase the contact area of the pad with the charging member is to make the pad larger. However, this idea has a disadvantage such that the image forming apparatus is upsized. Further, according to the Japanese Patent Laid-Open No. HEI 11-288150, a contact area of a cleaning unit for charging member that actually contributes to the cleaning of the charging member is small, thereby, a cleaning ability of the cleaning flexible member is not maintained for a long time. Furthermore, the main body of the image forming apparatus is provided with an intermediate transfer body, and therefore the photoreceptor does not contact the transfer paper directly. Thus, it is advantageous that quantity of the paper powder adhering to the transfer paper and reaching the charging member through the photoreceptor is small. This is disadvantageous, however, for a full color image forming apparatus in which the uneven charging tends to be conspicuous, because only one photoreceptor is provided for developing units of plural colors, and because the paper powder, though small in quantity, reaching the charging member through the intermediate transfer body and the photoreceptor, accumulates on one charging member.
The present invention has been achieved in order to solve the above-mentioned problems, and it is an object to provide an image forming apparatus capable of preventing stains on the charging roller, caused with the lapse of time, using an inexpensive mechanism. It is another object of the present invention to provide an image forming apparatus capable of prolonging lives of cleaning units and charging members, using an inexpensive mechanism.
The image forming apparatus according to the present invention, comprises a plurality of image carriers that carry toner images; an intermediate transfer body through which the toner images carried by the image carriers are transferred onto a recording medium; a plurality of charging members provided in contact with or adjacent to the image carriers, respectively, and a cleaning unit that is in contact with at least one of the changing member and removes foreign substances from a surface of the changing member.
The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.